The present invention relates generally to wind turbine blade moulds and particularly to the preparation method of glass reinforced, thermal expansion tolerable, electrically heated moulds.
In recent years, concern about global warming and the harmful effects of fuel emissions has created new demand for cleaner and sustainable energy sources, like wind. Wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Wind turbines harness the kinetic energy of wind and transform this kinetic energy into electrical energy. Thus, electrical power can be generated in an almost pollution free manner. To generate electrical power, wind turbines generally include a rotor that supports a number of blades extending radially therefrom. These blades capture the kinetic energy of the wind and, in turn, cause rotational motion of a drive shaft and a rotor of a generator. The amount of energy produced by such wind power generation systems is dependent on the ability of the wind turbine to capture wind and in turn depends on the physical and structural parameters of the rotor blades.
It is generally desirable to maintain good quality control standards over wind turbine blade design and manufacturing. Every rotor blade is a mirror image of the mould in which it is cast. The technology behind designing and building these moulds is therefore crucial for the quality of the finished blades. Once cast, the blade profile must be according to the dimension and quality specifications and have extremely limited variation between successive castings. Additionally, there are also stringent requirements about the process, including a rapid throughput time during casting.
To improve efficiency and speed in production of the rotor blades, greater control is required over the moulding process itself. The moulds need to be fitted with the heating feature to cure the components of the rotor blades, particularly the epoxy resins. The cure rate of the epoxy resins used in the blade manufacture is highly dependent upon temperature. The temperature of curing the resins can be up to about 130° C. Another benefit of heating moulds is the ability to post cure the epoxy resin system. Post curing is a process whereby a cured product is held at an elevated temperature for some time to improve the mechanical properties of the product by relieving stress. One exemplary post curing process is held at temperatures of about 65° C. to about 70° C. for a duration up to about 12 hours. The temperature should be controllable within the error of about ±3° C.
Therefore there is a need for a mould and a method of fabricating a mould that provides a robust heating solution without degrading the efficiency or the durability of the mould itself while enabling the desired repeatability and reproducibility of high quality moulded products, such as the wind blades discussed above.